1. Field of the Invention
This invention relates to an insulation material and more particularly to thermal and sound insulation material that includes a mineral wool batting interlaced with a plurality of nonflammable, heat sensitive organic fibers that bind together the fibers of the mineral wool batting to provide an insulation material having a preselected thickness and density with uniform tensile strength throughout.
2. Description of the Prior Art
Thermal and sound insulation, as illustrated and described in U.S. Pat. Nos. 2,579,035; 2,598,102; 2,612,162; 2,633,433; and 3,144,376 include a glass fiber batting in which felt-like layers are bound together by a resinous binder either of the thermosetting or the thermoplastic type, depending upon the particular characteristics desired for the insulation material.
The inorganic fibers are arranged in an interwoven relationship to form a fibrous layer of material having a preselected thickness and density. Formation of the felted structure from the mineral wool fibers is followed by the application of a thermosetting resin to the fibrous layers. The resins are generally applied in the form of an aqueous solution of a water-soluble liquid thermosetting resin in liquid form, an aqueous dispersion of a water insoluble thermosetting resin or in a dry, powdered, finely divided form.
The most commonly utilized thermosetting resins and binders for felted insulation material are phenol-formaldehyde, resorcinol-formaldehyde, urea-formaldehyde and furfural-formaldehyde. The composite body made up of the layer of felted inorganic fibers has an unset binder distributed throughout the fibers and is transferred to an oven where the fibers in the binder are subjected to a setting temperature, preferably in the range of about 400.degree. to 500.degree. F. for a preselected time interval. When the composite body leaves the oven, the binder is allowed to cool and harden at room temperature.
The use of thermosetting resins as binders for the inorganic fibers of the felted body present a substantial health hazard during the application of the binder. During the application stage, and particularly in the case of binders in dry, powdered form and liquid spray form, up to 10% of the material is lost and dispersed into the air constituting a deleterious working environment. Furthermore, material that is not dispersed into the air and is carried away in liquid form is frequently discharged as a water pollutant. In the case of an aqueous emulsion of the water insoluble thermosetting resin in liquid form, the emulsion breaks down when discharged as waste, and the resinous binder by-product presents a serious health hazard if permitted to contaminate a public water system. Additional losses take place as a consequence of vaporization during the curing operation. As much as a 5 to 10% loss will occur at this stage in addition to whatever losses occur during the application stage of the resinous binder to the felted body. Therefore, to accommodate the resultant losses, excess of resinous binder must be applied to assure that the minimum adhesion is obtained for the felted body.
In addition to forming insulating articles by the application of a bonding resin to nonwoven, inorganic fibers it has also been suggested, as disclosed in United States Pat. No. 3,660,222, to impregnate threads of synthetic polyester fibers with a binding resin. The fibrous webs are formed by the conventional process of carding or garnetting. The fibrous web is sprayed by a resinous bonding agent and cured to form a laminated body of polyester fibers. However, waste of materials and generation of pollutants occur in spraying the resinous liquid onto the surface of the fibrous web.
There is need for a thermal and sound insulating material fabricated by interlocking inorganic fibers to form a felted body or batting in which the fibers are adhesively bonded together to form a composite fibrous insulating material of a preselected thickness and density with substantially uniform tensile strength throughout. While it has been suggested by the prior art to bind the fibrous layers together by the application of a resinous binder in liquid or powder form, a substantial portion of the binder is lost upon application and curing. In addition, the curing must take place at temperatures in excess of 400.degree. F. presenting a considerable health hazard in the form of air and water pollution.